This invention relates to an antenna matching apparatus for a high-frequency transmitter which is speedily switchable between different transmitter frequencies according to a predetermined frequency scheme.
Radio transmission processes will often involve very rapid frequency changes by the transmitter. Frequency changing is a known practice for avoiding interferences in radio transmission. According to this practice, the transmitter is abruptly switched according to a frequency scheme which is a sequence of frequencies. The scheme used is the same as the scheme known and used by the receiver. Depending upon the value of the frequency band, the switching times that are possible with modern transmitters are on the order of milliseconds or even microseconds. The present invention strives for even shorter switching times.
The impedance of antennas operated with such frequency changing transmitters must be matched in their impedance with the output resistance of the transmitter. This is especially true for antennas that are small relative to the wave length and for those antennas used in mobile applications. Such antenna matching units include isolating circuits of high quality in which high idle powers occur. For this reason, in such matching units to switchover the reactances used here, the switches used must be able to switch relatively high powers. Switches, such as vacuum relays, used for relatively high power loads have relatively slow switching times. The more modern rapidly switching semiconductor switches cannot be used in these transmitters because of the high-power load requirements. The rapidity of the frequency switchover is therefore determined in these units exclusively by the rapidity at which the matching unit can be switched in frequency. In actual practice, at best switchover times of a few milliseconds can be attained. This is too slow for various applications, including those mentioned above, as well as many military applications.